Motor control device and steering device for vehicle

ABSTRACT

In a state in which the energization in the first direction is possible between the motor and the drive circuit and the motor is not rotating at high speed, when the phase induced voltage value of the specific phase that is the target of determination is continuously equal to or smaller than the abnormality determination threshold, the abnormality detecting unit determines that an open malfunction has occurred in the relay FET of the specific phase.

FIELD OF THE INVENTION

The present invention relates to a motor control device and a steering device for a vehicle.

BACKGROUND OF THE INVENTION

Patent Document 1 discloses a motor control device that controls a brushless motor, and a steering device for a vehicle in which the motor control device is used. According to the configuration disclosed in Patent Document 1, in power lines of a U phase, a V phase, and a W phase that connect a motor and a drive circuit (inverter), phase open switches, which cut off electric currents flowing to the phases, are respectively provided. From viewpoints of reduction in size, reduction in costs and the like, relay FETs formed of field effect transistors are used instead of conventional mechanical relay contacts in the phase open switches. The drive circuit is configured by connecting, with a pair of switching elements connected in series set as a basic unit (switching arm), three switching arms in parallel to correspond to motor coils of the respective phases.

In the FETs, parasitic diodes are present because of the structure of the FETs. Therefore, even if an open malfunction occurs in the relay FETs, energization in a first direction is allowed by the parasitic diodes. Therefore, in the configuration disclosed in Patent Document 1, a voltage is applied to only a specific phase in a state in which all the relay FETs respectively corresponding to the U phase, the V phase, and the W phase are turned on. Presence or absence of the open malfunction is determined according to whether a voltage based on the applied voltage is generated in the phases other than the specific phase. When the open malfunction is determined, only a switching element on a power supply side in the switching arm of the specific phase is turned on, whereby the voltage is applied to only the specific phase.

In this way, in the conventional configuration, the drive circuit is set to a special form different from a form during driving of the motor and a voltage is applied to the motor. Therefore, it is impossible to determine the open malfunction while driving the motor. That is, the open malfunction can be determined only under a limited situation during ignition-on or the like. Accordingly, when the open malfunction occurs during traveling of a vehicle, an abnormality of a control circuit cannot be quickly detected.

Note that Patent Document 2 discloses a method for detecting an energization failure that occurs when breaking of wire occurs in a power supply route between a motor and a drive circuit. Even with the method disclosed in Patent Document 2, the open malfunction of the control circuit cannot be detected.

-   Patent Document 1: Japanese Patent Application Laid-Open No.     2009-261067 -   Patent Document 2: Japanese Patent Application Laid-Open No.     2007-244028

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a motor control device and a steering device for a vehicle that can detect an open malfunction of a phase open switch even during driving of a motor.

In order to solve the problem, according to a first aspect of the present invention, there is provided a motor control device including: motor control signal output means for outputting a motor control signal; a drive circuit configured to supply drive power of three phases to a motor on the basis of the motor control signal; phase open switches provided in power lines of respective phases that connect the motor and the drive circuit; and abnormality detecting means for detecting an open malfunction of the phase open switches on the basis of a voltage parameter equivalent to a voltage applied to the motor. The motor control signal output means outputs the motor control signal by executing current feedback control in order to cause an actual current value to follow a current command value, which is a target value of an electric current supplied to the motor. In the motor control device, the phase open switches include parasitic diodes that allow energization in a first direction in an OFF state for cutting off energization to phase corresponding to the phase open switches. In a state in which the energization in the first direction is possible between the motor and the drive circuit and the motor is not rotating at high speed, when the voltage parameter of a specific phase set as a determination target increases to a side for feeding an electric current in a second direction in which energization is not allowed by the parasitic diodes and exceeds an abnormality determination threshold, the abnormality detecting means determines that an open malfunction has occurred in the phase open switch of the specific phase.

According to this configuration, even if the open malfunction occurs in the phase open switches, the energization in the first direction is allowed by the presence of the parasitic diodes and only the energization in the second direction is cut off. Therefore, when the open malfunction occurs in the configuration for executing current feedback control, the voltage parameter increases to a side for feeding an electric current at least in the second direction. In a state in which the motor is rotating at high speed, even if the open malfunction has not occurred, an electric current cannot be fed to the motor because of the influence of an induced voltage. Therefore, the voltage parameter increases.

That is, in the state in which the energization in the first direction is possible between the motor and the drive circuit and the motor is not rotating at high speed, when the voltage parameter of the specific phase increases exceeding the abnormality determination threshold to a side for feeding an electric current in the second direction, it is possible to determine that the open malfunction has occurred in the phase open switch of the specific phase. Such determination is not performed by applying a voltage to the motor in a special form but is performed on the basis of a change in the voltage parameter during current feedback control. Therefore, the determination can be performed during driving of the motor. Accordingly, it is possible to detect the open malfunction while driving the motor and quickly attain failsafe.

In the motor control device, it is preferable that the abnormality detecting means determines whether the motor is rotating at high speed when a sign of the voltage parameter of the specific phase changes from a sign indicating feeding of an electric current in the first direction to a sign indicating feeding of an electric current in the second direction, and, when the voltage parameter of at least one phase among the phases other than the specific phase exceeds a high-speed determination threshold based on an induced voltage, which occurs during high-speed rotation, in one cycle of electrical angle before the change of the voltage parameter of the specific phase to the sign indicating feeding of an electric current in the second direction, the abnormality detecting means determines that the motor is rotating at high speed.

As explained above, during the high-speed rotation of the motor, the voltage parameter increases according to the influence of the induced voltage. Therefore, according to this configuration, by determining whether the voltage parameter exceeds the high-speed determination threshold, it is possible to determine, without using a rotation angle sensor, with a simple configuration, whether the motor is rotating at high speed. The determination as to whether the motor is rotating at high speed is performed when the sign of the voltage parameter changes to the sign indicating feeding of an electric current in the second direction. Therefore, before the voltage parameter changes to a state likely to exceed the abnormality determination threshold, it is possible to determine whether the motor is rotating at high speed.

In the motor control device, it is preferable that, when the voltage parameter of at least one phase of the other phases exceeds the high-speed determination threshold while the sign of the voltage parameter of the specific phase in the one cycle of electrical angle is the sign indicating feeding of an electric current in the first direction, the abnormality detecting means determines that the motor is rotating at high speed.

As explained above, in a state in which the open malfunction has occurred in the phase open switch of the specific phase, the voltage parameter has an abnormal value when an electric current is fed in the second direction. It is likely that a change in the voltage parameters of the other phases become unstable while the sign of the voltage parameter of the specific phase indicates feeding of an electric current in the second direction. In this regard, according to this configuration, while the sign of the voltage parameter of the specific phase indicates feeding of an electric current in the first direction, that is, in a state in which the voltage parameter of the specific phase does not have an abnormal value, it is determined whether the voltage parameters of the other phases exceed the high-speed determination threshold. Therefore, a change in the voltage parameters of the other phases less easily becomes unstable. It is possible to accurately perform determination of high-speed rotation.

In the motor control device, it is preferable that the abnormality detecting means uses, as the voltage parameter, phase induced voltage values calculated on the basis of phase current values and phase voltage values of the motor.

Phase voltage values, which are voltages applied to the phases, are sums of multiplied values of phase current values, which are actual current values supplied to the motor, and resistance values of the phases and the phase induced voltage values. Therefore, when an electric current supplied to the motor is large, even if the open malfunction has not occurred, it is likely that the voltage parameter increases exceeding the abnormality determination threshold to a side for feeding an electric current in the second direction. In this regard, according to this configuration, since the phase induced voltage values obtained by subtracting the multiplied values from the phase voltage values are used as the voltage parameters, it is possible to accurately determine the open malfunction.

In the motor control device, it is preferable that, when the voltage parameter is equal to or smaller than an energization determination threshold set to a side for feeding an electric current in the first direction, the abnormality detecting means determines that the energization in the first direction is possible between the motor and the drive circuit.

According to this configuration, it is possible to easily determine whether the energization in the first direction is possible.

In the motor control device, it is preferable that, when an energization failure has not occurred in a power supply route between the motor and the drive circuit, the abnormality detecting means determines that the energization in the first direction is possible between the motor and the drive circuit.

According to this configuration, when a determination result of the energization failure is used, it is unnecessary to separately perform determination as to whether the energization in the first direction is possible.

In order to solve the problem, according to a second aspect of the present invention, a steering device for a vehicle including the motor control device is provided.

According to the configuration, it is possible to detect the open malfunction of the phase open switches even during driving of the motor. Therefore, it is possible to suppress, for example, deterioration in steering feeling by quickly attaining failsafe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the configuration of an electric power steering device (EPS).

FIG. 2 is a control block diagram of an ECU.

FIG. 3 is a control block diagram of a microcomputer.

FIG. 4(a) is a waveform chart showing a phase induced voltage value of a specific phase in a state in which a motor is not rotating at high speed

FIG. 4(b) is a waveform chart showing phase induced voltage values in a state in which the motor is rotating at high speed.

FIG. 5 is a flowchart for explaining a processing procedure of abnormality determination by an abnormality detecting unit.

FIG. 6 is a flowchart for explaining a processing procedure of open malfunction determination by the abnormality detecting unit.

FIG. 7 is a flowchart for explaining a processing procedure of high-speed rotation determination by the abnormality detecting unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment in which a steering device for a vehicle according to the present invention is embodied as an electric power steering device (EPS) 1 is explained below with reference to the drawings.

As shown in FIG. 1, a steering wheel 2 is fixed to a steering shaft 3 and coupled to a rack shaft 5 via a rack and pinion mechanism 4. When a driver operates the steering wheel 2, the steering shaft 3 rotates and the rotation of the steering shaft 3 is converted into a reciprocating linear motion of the rack shaft 5 via the rack and pinion mechanism 4. The steering shaft 3 is configured by coupling a column shaft 8, an intermediate shaft 9, and a pinion shaft 10. Tie rods 11 are respectively coupled to both ends of the rack shaft 5. The reciprocating linear motion of the rack shaft 5 is transmitted to a not-shown knuckle via the tie rods 11. Consequently, a steering angle of turning wheels 12 is changed and a traveling direction of a vehicle is changed.

The EPS 1 includes an EPS actuator 22 functioning as a steering force assisting device and an ECU 23 functioning as a motor control device. The EPS actuator 22 gives an assist force for assisting steering operation to a steering system. The ECU 23 controls the actuation of the EPS actuator 22.

The EPS actuator 22 is configured as an EPS actuator of a column assist type. The EPS actuator 22 includes a motor 21 functioning as a driving source and a deceleration mechanism 25 configured from a worm, a wheel, and the like. The motor 21 is coupled to the column shaft 8 via the deceleration mechanism 25. A brushless motor is adopted as the motor 21. The motor 21 is driven by the supply of drive power of three phases (U, V, and W) from the ECU 23. The EPS actuator 22 decelerates the rotation of the motor 21 and transmits the rotation to the column shaft 8. Consequently, the torque of the motor 21 is given to the steering system as an assist force.

A torque sensor 27 configured to detect steering torque T and a vehicle speed sensor 28 configured to detect vehicle speed SPD are connected to the ECU 23. The ECU 23 calculates a target assist force on the basis of the steering torque T and the vehicle speed SPD. The ECU 23 supplies driving electric power to the motor 21 in order to generate motor torque equivalent to the target assist force. In this way, the ECU 23 controls the actuation of the EPS actuator 22 and executes power assist control.

The electrical configuration of the EPS 1 is explained with reference to FIG. 2.

As shown in FIG. 2, the ECU 23 includes a microcomputer 31 functioning as motor control signal output means and a drive circuit 32. The microcomputer 31 outputs a motor control signal. The drive circuit 32 supplies drive power of three phases to the motor 21 on the basis of the motor control signal output from the microcomputer 31. Control blocks explained below are realized by a computer program executed by the microcomputer 31. The microcomputer 31 detects state amounts at a predetermined sampling cycle. The microcomputer 31 executes respective kinds of arithmetic processing at each predetermined arithmetic operation cycle and outputs a motor control signal.

The drive circuit 32 is configured by connecting a plurality of FETs (field effect transistors) 33 a to 33 f functioning as switching elements. The drive circuit 32 is configured by connecting, in parallel, series circuits of pairs of the FETs 33 a and 33 d, the FETs 33 b and 33 e, and the FETs 33 c and 33 f. Connection points of the FETs 33 a and 33 d, the FETs 33 b and 33 e, and the FETs 33 c and 33 f are respectively connected to motor coils 35 u, 35 v, and 35 w of the phases of the motor 21 via power lines 34 u, 34 v, and 34 w. That is, the drive circuit 32 is configured as a well-known PWM inverter configured by connecting, with a pair of switching elements connected in series set as a basic unit (switching arm), three switching arms corresponding to the phases in parallel. The motor control signal output from the microcomputer 31 is a gate ON/OFF signal specifying switching states of the FETs 33 a to 33 f.

The FETs 33 a to 33 f are turned on and off in response to the motor control signal applied to gate terminals. In this way, an energization pattern to the motor coils 35 u, 35 v, and 35 w of the phases is switched, whereby a power supply voltage of a vehicle-mounted power supply (battery) 36 is converted into drive power of the three phases (U, V, and W) and output to the motor 21.

Current sensors 37 u, 37 v, and 37 w and voltage sensors 38 u, 38 v, and 38 w are provided halfway in the power lines 34 u, 34 v, and 34 w. The current sensors 37 u, 37 v, and 37 w respectively detect phase current values Iu, Iv, and Iw of the motor 21. The voltage sensors 38 u, 38 v, and 38 w respectively detect phase voltage values Vu, Vv, and Vw of the motor 21. Relay FETs 39 u, 39 v, and 39 w functioning as phase open switches for setting the phases to an open state in which energization is impossible are respectively provided halfway in the power lines 34 u, 34 v, and 34 w.

The relay FETs 39 u, 39 v, and 39 w are turns on and off in response to a relay control signal output from the microcomputer 31. The relay FETs 39 u, 39 v, and 39 w change to an ON state to enable energization to the phases corresponding thereto and change to an OFF state to cut off energization to the phases corresponding thereto. In the relay FETs 39 u, 39 v, and 39 w, parasitic diodes D are present because of the structure of the relay FETs 39 u, 39 v, and 39 w. The relay FETs 39 u, 39 v, and 39 w are provided such that the parasitic diodes D allow energization in a direction from the drive circuit 32 to the motor 21. MOSFETs are adopted as the relay FETs 39 u, 39 v, and 39 w.

A rotation angle sensor (resolver) 40 for detecting a motor rotation angle θm of the motor 21 is connected to the microcomputer 31 together with the current sensors 37 u, 37 v, and 37 w and the voltage sensors 38 u, 38 v, and 38 w. As shown in FIG. 3, the microcomputer 31 includes a motor control unit 41 related to the control of the motor 21 and a relay control unit 42 related to the control of the relay FETs 39 u, 39 v, and 39 w. An ignition signal S_IG indicating an ON/OFF state of an ignition switch (IG) of the vehicle is input to the relay control unit 42. When the ignition signal S_IG indicates IG ON, the relay control unit 42 outputs a relay control signal for turning on the relay FETs 39 u, 39 v, and 39 w. On the other hand, when the ignition signal S_IG indicates IG OFF, the relay control unit 42 outputs a relay control signal for turning off the relay FETs 39 u, 39 v, and 39 w.

The motor control unit 41 includes a current command value calculating unit 44 and a motor control signal output unit 45. The current command value calculating unit 44 calculates a current command value (q-axis current command value Iq*) corresponding to a target value of power supply to the motor 21, that is, a target assist force. The motor control signal output unit 45 outputs a motor control signal on the basis of the current command value.

The steering torque T and the vehicle speed SPD are input to the current command value calculating unit 44. The current command value calculating unit 44 calculates, on the basis of the steering torque T and the vehicle speed SPD, the q-axis current command value Iq* in a two-phase rotational coordinate system (d/q coordinate system) as the current command value. The d/q coordinate system is a coordinate system conforming to the motor rotation angle θm. Specifically, the current command value calculating unit 44 calculates the q-axis current command value Iq* having a larger value (absolute value) as (an absolute value of) the steering torque T is larger or the vehicle speed SPD is lower. The d-axis current command value Id* is fixed to zero (Id*=0).

The phase current values Iu, Iv, and Iw and the motor rotation angle θm are input to the motor control signal output unit 45 together with the q-axis current command value Iq*. The motor control signal output unit 45 executes current feedback control in the d/q coordinate system on the basis of these state values to thereby generate the motor control signal.

Specifically, the phase current values Iu, Iv, and Iw input to the motor control signal output unit 45 are input to a d/q conversion unit 51. The d/q conversion unit 51 maps the phase current values Iu, Iv, and Iw onto a d/q coordinate on the basis of the motor rotation angle θm to thereby calculate a d-axis current value Id and a q-axis current value Iq. Subsequently, the q-axis current value Iq is input to a subtracter 52 q together with the q-axis current command value Iq* input from the current command value calculating unit 44. The d-axis current value Id is input to a subtracter 52 d together with the d-axis current command value Id*. The subtracters 52 d and 52 q respectively calculate a d-axis current deviation ΔId and a q-axis current deviation ΔIq.

The d-axis current deviation ΔId and the q-axis current deviation ΔIq are respectively input to F/B (feedback) control units 53 d and 53 q corresponding thereto. The F/B control units 53 d and 53 q execute a feedback calculation in order to cause the d-axis current value Id and the q-axis current value Iq, which are actual current values, to follow the d-axis current command value Id* and the q-axis current command value Iq*. Consequently, the F/B control units 53 d and 53 q respectively calculate a d-axis voltage command value Vd* and a q-axis voltage command value Vq*, which are voltage command values of the d/q coordinate system. Specifically, the F/B control units 53 d and 53 q respectively multiply the d-axis current deviation ΔId and the q-axis current deviation ΔIq with a proportional gain to calculate proportional components. The F/B control units 53 d and 53 q respectively multiply the d-axis current deviation ΔId and the q-axis current deviation ΔIq with an integral gain to calculate integral components. The F/B control units 53 d and 53 q respectively add up the proportional components and the integral components to calculate the d-axis voltage command value Vd* and the q-axis voltage command value Vq*.

The d-axis voltage command value Vd* and the q-axis voltage command value Vq* are input to a d/q inverse conversion unit 54 together with the motor rotation angle θm. The d/q inverse conversion unit 54 maps the d-axis voltage command value Vd* and the q-axis voltage command value Vq* onto an alternating-current coordinate of the three phases on the basis of the motor rotation angle θm to thereby respectively calculate phase voltage command values Vu*, Vv*, and Vw* of the three phases. Subsequently, the phase voltage command values Vu*, Vv*, and Vw* are input to a PWM command value calculating unit 55. The PWM command value calculating unit 55 calculates DUTY command values αu, αv, and αw of the phases respectively on the basis of the phase voltage command values Vu*, Vv*, and Vw* and outputs the DUTY command values αu, αv, and αw to a PWM output unit 56. The PWM output unit 56 generates a motor control signal having an On DUTY ratio indicated by the DUTY command values αu, αv, and αw and outputs the motor control signal to the drive circuit 32. Consequently, drive power corresponding to the motor control signal is output to the motor 21. Motor torque corresponding to the drive power (energization current amount) is given to the steering system as an assist force.

Abnormality detection by the ECU 23 is explained with reference to FIGS. 2 and 3.

As shown in FIG. 3, an abnormality detecting unit 71 functioning as abnormality detecting means is provided in the microcomputer 31. The abnormality detecting unit 71 detects an energization failure of a power supply route for supplying drive power to the motor 21 and an open malfunction (open fixed malfunction) in which the relay FETs 39 u, 39 v, and 39 w remain in the OFF state and do not change to the ON state. Examples of a form of the energization failure include a disconnection failure of the power lines 34 u, 34 v, and 34 w and an open malfunction of the FETs 33 a to 33 f that configure the drive circuit 32. As shown in FIG. 2, in a phase in which the energization failure occurs, energization is cut off in both of a direction from the drive circuit 32 to the motor 21 (first direction) and a direction from the motor 21 to the drive circuit 32 (second direction). When the open malfunction occurs in the relay FETs 39 u, 39 v, and 39 w, the energization in the first direction is allowed by the presence of the parasitic diodes D.

As shown in FIG. 3, the phase current values Iu, Iv, and Iw and the phase voltage values Vu, Vv, and Vw are input to the abnormality detecting unit 71. The abnormality detecting unit 71 calculates phase induced voltage values eu, ev, and ew as voltage parameters, which are equivalent to a voltage applied to the motor 21, respectively on the basis of the phase current values Iu, Iv, and Iw and the phase voltage values Vu, Vv, and Vw by using the following Expressions (1) to (3). eu=Vu−Iu·Ru  (1) ev=Vv−Iv·Rv  (2) ew=Vw−Iw·Rw  (3)

Expressions (1) to (3) are well-known motor voltage equations. In the expressions, “Ru”, “Rv”, and “Rw” indicate resistance values of the motor coils 35 u, 35 v, and 35 w of the phases.

The abnormality detecting unit 71 sets one phase of the three phases as a specific phase on the basis of the phase induced voltage values eu, ev, and ew and determines, for each of the phases, whether an abnormality has occurred. The abnormality detecting unit 71 outputs an abnormality detection signal S_pde indicating a result of the determination respectively to the motor control unit 41 and the relay control unit 42. The abnormality detecting unit 71 simultaneously executes abnormality detection for the phases in parallel. Consequently, when the abnormality detection signal S_pde indicating that some abnormality has occurred is output, the motor control unit 41 stops the motor 21. The relay control unit 42 turns off the relay FETs 39 u, 39 v, and 39 w. Consequently, failsafe is quickly performed.

As indicated by a solid line in FIG. 4(a), in a state in which the open malfunction has not occurred and the motor 21 is not rotating at high speed, a phase induced voltage value ex of a specific phase (X phase) set as a determination target does not increase to both plus and minus sides. “X” indicates any one phase of the three phases U, V, and W. In this embodiment, a sign of the phase induced voltage value ex is plus when an electric current is fed in the first direction and is minus when an electric current is fed in the second direction.

On the other hand, when the open malfunction occurs in a relay FET 39× of the specific phase, the energization in the first direction is allowed by the presence of the parasitic diodes D. Only the energization in the second direction is cut off. Therefore, even if the open malfunction occurs in a configuration for executing current feedback control, when an electric current is fed in the first direction, the d-axis current deviation ΔId and the q-axis current deviation ΔIq do not increase and the phase induced voltage value ex does not increase to the plus side. On the other hand, when an electric current is fed in the second direction, as indicated by a broken line in FIG. 4(a), since the d-axis current deviation ΔId and the q-axis current deviation ΔIq increase, the phase induced voltage value ex increase to the minus side.

That is, since the energization in the first direction is allowed even in a state in which the open malfunction occurs, usually, the phase induced voltage value ex of the specific phase is not equal to or larger than an energization determination threshold e_pd set to a plus value. On the other hand, since the energization in the second direction is cut off in the state in which the open malfunction occurs, the phase induced voltage value ex of the specific phase is equal to or smaller than an abnormality determination threshold e_er set to a minus value. The energization determination threshold e_pd and the abnormality determination threshold e_er respectively have magnitudes, which cannot be usually taken, in a state in which the motor 21 is not rotating at high speed and the energization in the second direction is allowed. The magnitudes of the energization determination threshold e_pd and the abnormality determination threshold e_er may be the same or may be different.

As shown in FIG. 4(b), in a state in which the motor 21 is rotating at high speed, even if the open malfunction of the relay FETs 39 u, 39 v, and 39 w has not occurred, the phase induced voltage values eu, ev, and ew are equal to or larger than a high-speed determination threshold e_hip set to a plus value or equal to or smaller than a high-speed determination threshold e_him set to a minus value. The high-speed determination thresholds e_hip and e_him are values based on an induced voltage generated during high-speed rotation when the motor 21 can be regarded as stably rotating. The high-speed determination thresholds e_hip and e_him are set to values smaller than the energization determination threshold e_pd and the abnormality determination threshold e_er.

Based on this point, the abnormality detecting unit 71 determines that in a state in which the relay FET 39× is controlled to be turned off and it is determined that the energization in the first direction is possible and the motor 21 is not rotating at high speed, when the phase induced voltage value ex of the specific phase is continuously large exceeding the abnormality detection threshold e_er to the minus side, that is, when the phase induced voltage value ex is continuously equal to or smaller than the abnormality determination threshold e_er, the open malfunction has occurred in a relay FET 39× of the specific phase. Note that the relay FETs 39 u, 39 v, and 39 w are controlled to be turned on during IG ON. Therefore, the abnormality detecting unit 71 determines the open malfunction assuming that the relay FETs 39 u, 39 v, and 39 w are controlled to be turned on.

More specifically, when the phase induced voltage value ex of the specific phase is equal to or smaller than the energization determination threshold e_pd, the abnormality detecting unit 71 determines that the energization in the first direction is possible. When the energization in the first direction is possible, the abnormality detecting unit 71 determines whether the open malfunction has occurred in the relay FET 39× of the phase. In the determination, first, the abnormality detecting unit 71 performs, on the basis of the phase induced voltage values eu, ev, and ew, high-speed rotation determination for determining whether the motor 21 is rotating at high speed.

Specifically, the abnormality detecting unit 71 determines whether phase induced voltage values ey and ez of the other phases (Y phase and Z phase) are equal to or smaller than the high-speed determination threshold e_him while a sign of the phase induced voltage value ex of the specific phase is plus. “Y” indicates one phase other than “X” among the three phases U, V, and W. “Z” indicates the remaining one phase other than “X” and “Y” among the three phases U, V, and W. When at least one of the phase induced voltage values ey and ez of the other phases exceeds the high-speed determination threshold e_him, when the sign of the phase induced voltage value ex of the specific phase changes from plus to minus, the abnormality detecting unit 71 determines that the motor 21 is rotating at high speed. The abnormality detecting unit 71 determines that the sign of the phase induced voltage value ex is plus when the phase induced voltage value ex is larger than a sign determination threshold e_0 and determines that the sign of the phase induced voltage value ex is minus when the phase induced voltage value ex is equal to or smaller than the sign determination threshold e_0. The sign determination threshold e_0 is set to a value near zero taking into account a detection error and the like.

When it is determined that the motor 21 is not rotating at high speed, the abnormality detecting unit 71 measures the number of times of abnormality the phase induced voltage value ex is equal to or smaller than the abnormality determination threshold e_er set to a minus value. When the number of times of abnormality exceeds a predetermined number of times, the abnormality detecting unit 71 determines that the open malfunction has occurred. On the other hand, when it is determined that the motor 21 is rotating at high speed, the abnormality detecting unit 71 clears the number of times of abnormality and measures the number of times of abnormality again. When the number of times of abnormality does not increase for a predetermined time or more after the phase induced voltage value ex is equal to or smaller than the abnormality determination threshold e_er once, the abnormality detecting unit 71 also clears the number of times of abnormality (time over). Consequently, it is possible to prevent a situation in which the number of times the phase induced voltage value ex is equal to or smaller than the abnormality determination threshold e_er is multiplied because of the influence of noise or the like and it is erroneously determined that the open malfunction has occurred.

On the other hand, when the phase induced voltage value ex of the specific phase is larger than the energization determination threshold e_pd, the energization in the first direction is cut off, and it is likely that an energization failure has occurred, the abnormality detecting unit 71 determines the energization failure. The determination of the energization failure is performed by a well-known method based on whether an electric current is not flowing, although it is attempted to feed an electric current to the motor 21. When a phase current value Ix is equal to or smaller than a predetermined current value Ith, when the DUTY command value αx is a value outside a predetermined range corresponding to the predetermined current value Ith, the abnormality detecting unit 71 determines that the energization failure has occurred. The predetermined current value Ith is a value indicating a non-energization state and is set to a value larger than zero taking into account a detection error and the like. The predetermined range is a range of the DUTY command value ax in which the phase current value Ix should be equal to or smaller than the predetermined current value Ith in a state in which an induced voltage is not high. The predetermined range is also set taking into account a detection error and the like.

A processing procedure of abnormality determination by the abnormality detecting unit is explained with reference to flowcharts of FIGS. 5 to 7.

As shown in FIG. 5, the abnormality detecting unit 71 acquires the phase current values Iu, Iv, and Iw and the phase voltage values Vu, Vv, and Vw (step 201). Subsequently, the abnormality detecting unit 71 calculates the phase induced voltage values eu, ev, and ew on the basis of Expressions (1) to (3) (step 202). Subsequently, the abnormality detecting unit 71 determines whether the phase induced voltage value ex of the X phase (e.g., the U phase), which is the specific phase, is equal to or smaller than the energization determination threshold e_pd (step 203). When the phase induced voltage value ex is equal to or smaller than the energization determination threshold e_pd (step 203: YES), the abnormality detecting unit 71 determines whether an open malfunction of the relay FET 39× has occurred (step 204). On the other hand, when the phase induced voltage value ex is larger than the energization determination threshold e_pd (step 203: NO), the abnormality detecting unit 71 determines whether an energization failure has occurred (step 205). The energization failure determination is a well-known method. Therefore, detailed explanation of a processing procedure is omitted.

A processing procedure of the open malfunction determination in step 204 is explained.

As shown in FIG. 6, first, the abnormality detecting unit 71 performs high-speed rotation determination for determining whether the motor 21 is rotating at high speed (step 301). As a result, the abnormality detecting unit 71 determines whether a high-speed rotation flag indicating that the motor 21 is rotating at high speed is set (step 302). When the high-speed rotation flag is not set (step 302: NO), the abnormality detecting unit 71 determines whether the phase induced voltage value ex of the specific phase is equal to or smaller than the abnormality determination threshold e_er (step 303).

Subsequently, when the phase induced voltage value ex is equal to or smaller than the abnormality determination threshold e_er (step 303: YES), the abnormality detecting unit 71 determines whether a continuation flag indicating that a state in which the phase induced voltage value ex is equal to or smaller than the abnormality determination threshold e_er continues is set (step 304). When the continuation flag is not set (step 304: NO), the abnormality detecting unit 71 sets the continuation flag (step 305), clears an abnormality counter (step 306: C=0), and then increments the abnormality counter (step 307: C=C+1). On the other hand, when the continuation flag is set (step 304: YES), the abnormality detecting unit 71 shifts to step 307 and increments the abnormality counter without executing the processing in steps 305 and 306. Subsequently, the abnormality detecting unit 71 clears a timer value t of a not-shown timer for measuring a time interval of the increment of the abnormality counter (step 308) and determines whether a counter value C of the abnormality counter is equal to or larger than a predetermined number of times Cth (step 309). When the count value C is equal to or larger than the predetermined number of times Cth (step 309: YES), the abnormality detecting unit 71 determines that the open malfunction has occurred (step 310). When the count value C is smaller than the predetermined number of times Cth (step 309: NO), the abnormality detecting unit 71 does not determine that the open malfunction has occurred.

On the other hand, when the phase induced voltage value ex of the specific phase is larger than the abnormality determination threshold e_er (step 303: NO), the abnormality detecting unit 71 determines whether the continuation flag is set (step 311). When the continuation flag is set (step 311: YES), the abnormality detecting unit 71 acquires the timer value t (step 312). The abnormality detecting unit 71 determines whether the timer value t is larger than a predetermined timer value tth indicating a predetermined time (step 313). When the timer value t is larger than the predetermined timer value tth (step 313: YES), the abnormality detecting unit 71 clears the continuation flag (step 314) and clears the abnormality counter (step 315: C=0). When the high-speed rotation flag is set (step 302: YES), the abnormality detecting unit 71 also shifts to steps 314 and 315 and clears the continuation flag and the abnormality counter. On the other hand, when the continuation flag is not set (step 311: NO) and when the timer value t is equal to or smaller than the predetermined timer value tth (step 313: NO), the abnormality detecting unit 71 retains the continuation flag and the count value C of the abnormality counter.

A processing procedure of the high-speed rotation determination in step 301 is explained.

As shown in FIG. 7, first, the abnormality detecting unit 71 determines whether the high-speed rotation flag is set (step 401). When the high-speed rotation flag is not set (step 401: NO), the abnormality detecting unit 71 determines whether a Y-phase history flag indicating that the phase induced voltage value ey of the Y phase (e.g., the V phase), which is the other phase, is equal to or smaller than the high-speed determination threshold e_him is set (step 402). When the Y-phase history flag is not set (step 402: NO), the abnormality detecting unit 71 determines whether a Z-phase history flag indicating that the phase induced voltage value ez of the Z phase (e.g., the W phase), which is the other phase, is equal to or smaller than the high-speed determination threshold e_him is set (step 403). When the Z-phase history flag is not set (step 403: NO), the abnormality detecting unit 71 determines whether the phase induced voltage value ex of the specific phase is equal to or larger than the sign determination threshold e_0 (step 404).

Subsequently, when the phase induced voltage value ex is larger than the sign determination threshold e_0, that is, a sign of the phase induced voltage value ex is plus (step 404: YES), the abnormality detecting unit 71 determines whether the phase induced voltage value ey of the Y phase is equal to or smaller than the high-speed determination threshold e_him set to a minus value (step 405). When the phase induced voltage value ey is equal to or smaller than the high-speed determination threshold e_him (step 405: YES), the abnormality detecting unit 71 sets the Y-phase history flag (step 406), shifts to step 407, and determines whether the phase induced voltage value ez of the Z phase is equal to or smaller than the high-speed determination threshold e_him (step 407). When the phase induced voltage value ey is larger than the high-speed determination threshold e_him (step 405: NO), the abnormality detecting unit 71 shifts to step 407 without setting the Y-phase history flag. Subsequently, when the phase induced voltage value ez is equal to or smaller than the high-speed determination threshold e_him (step 407: YES), the abnormality detecting unit 71 sets the Z-phase history flag (step 408). On the other hand, when the phase induced voltage value ez is larger than the high-speed determination threshold e_him (step 407: NO), the abnormality detecting unit 71 does not set the Z-phase history flag. When the phase induced voltage value ex of the specific phase is equal to or smaller than the sign determination threshold e_0, that is, when a sign of the phase induced voltage value ex is minus (step 404: NO), the abnormality detecting unit 71 does not execute the processing in steps 405 to 408.

Subsequently, when the Y-phase history flag is set (step 402: YES) and when the Z-phase history flag is set (step 403: YES), the abnormality detecting unit 71 determines whether the sign of the phase induced voltage value ex of the specific phase is inverted. Specifically, the abnormality detecting unit 71 determines whether a last value ex_b of the phase induced voltage value ex stored in a not-shown memory is larger than the sign determination threshold e_0 (step 409). When the last value ex_b is larger than the sign determination threshold e_0 (step 409: YES), the abnormality detecting unit 71 determines whether the phase induced voltage value ex, which is a latest value, is equal to or smaller than the sign determination threshold e_0 (step 410). When the phase induced voltage value ex is equal to or smaller than the sign determination threshold e_0 (step 410: YES), the abnormality detecting unit 71 sets the high-speed rotation flag (step 411) and clears the Y-phase history flag and the Z-phase history flag (steps 412 and 413). When the last value ex_b is equal to or smaller than the sign determination threshold e_0 (step 409: NO) and when the phase induced voltage value ex is larger than the sign determination threshold e_0 (step 410: NO), the abnormality detecting unit 71 does not execute the processing in steps 411 to 413.

Subsequently, when the high-speed rotation flag is set (step 401: YES), the abnormality detecting unit 71 determines whether the phase induced voltage value ex of the specific phase is larger than the sign determination threshold e_0 (step 414). When the phase induced voltage value ex is larger than the sign determination threshold e_0 (step 414: YES), the abnormality detecting unit 71 clears the high-speed rotation flag (step 415). When the phase induced voltage value ex is equal to or smaller than the sign determination threshold e_0 (step 414: NO), the abnormality detecting unit 71 does not clear the high-speed rotation flag.

As explained above, according to this embodiment, it is possible to attain action and effects explained below.

(1) In a state in which the energization in the first direction is possible between the motor 21 and the drive circuit 32 and the motor 21 is not rotating at high speed, when the phase induced voltage value ex of the specific phase is continuously equal to or smaller than the abnormality determination threshold e_er, the abnormality detecting unit 71 determines that an open malfunction has occurred in the relay FET 39× of the specific phase. According to the configuration, since it is possible to determine on the basis of a change in the phase induced voltage value ex during current feedback control whether the open malfunction has occurred without applying a voltage to the motor 21 in a special form, it is possible to determine the open malfunction while driving the motor 21. Consequently, it is possible to quickly attain failsafe and suppress deterioration in steering feeling.

(2) The abnormality detecting unit 71 determines whether the phase induced voltage values ey and ez of the other phases exceed the high-speed determination threshold e_him while the sign of the phase induced voltage value ex of the specific phase is plus. When at least one of the phase induced voltage values ey and ez of the other phases exceeds the high-speed determination threshold e_him, when the sign of the phase induced voltage value ex of the specific phase changes from plus to minus, the abnormality detecting unit 71 determines that the motor 21 is rotating at high speed. According to the configuration, it is possible to determine, without using a rotation angle sensor, with a simple configuration, whether the motor 21 is rotating at high speed. Since the determination as to whether the motor 21 is rotating at high speed is performed when the sign of the phase induced voltage value exchanges to minus, before the phase induced voltage value ex of the specific phase changes to a state in which the phase induced voltage value ex is likely to exceed the abnormality determination threshold e_er, it is possible to determine whether the motor 21 is rotating at high speed.

In a state in which the open malfunction occurs in the relay FET 39× of the specific phase as explained above, when an electric current is about to be fed in the second direction, the phase induced voltage value ex of the specific phase is equal to or smaller than the abnormality determination threshold e_er. Therefore, while the sign of the phase induced voltage value ex is minus, it is likely that a change in the phase induced voltage values ey and ez of the other phases becomes unstable. In this regard, according to the configuration, while the sign of the phase induced voltage value ex of the specific phase is plus, that is, in a state in which the phase induced voltage value ex of the specific phase is not an abnormal value, it is possible to determine whether the phase induced voltage values ey and ez of the other phases exceed the high-speed determination threshold e_him. Therefore, it is possible to accurately perform the determination of the high-speed rotation.

(4) The abnormality detecting unit 71 calculates the phase induced voltage values eu, ev, and ew on the basis of the phase current values Iu, Iv, and Iw and the phase voltage values Vu, Vv, and Vw by using Expressions (1) to (3). The abnormality detecting unit 71 uses the phase induced voltage values eu, ev, and ew as the voltage parameters equivalent to the applied voltage applied to the motor 21. That is, the phase voltage values Vu, Vv, and Vw are sums of multiplied values of the phase current values Iu, Iv, and Iw and the resistance values Ru, Rv, and Rw and the phase induced voltage values eu, ev, and ew (see Expressions (1) to (3)). Therefore, if the phase voltage values Vu, Vv, and Vw are used as the voltage parameters, when an electric current supplied to the motor 21 is large, even if the open malfunction has not occurred, it is likely that the phase induced voltage values Vu, Vv, and Vw increase exceeding the abnormality determination threshold e_er to the minus side. In this regard, according to the configuration, since the phase induced voltage values eu, ev, and ew obtained by subtracting the multiplied values from the phase voltage values Vu, Vv, and Vw are used as the voltage parameters, it is possible to accurately determine the open malfunction.

(5) When the phase induced voltage value ex is equal to or smaller than the energization determination threshold e_pd, the abnormality detecting unit 71 determines that the energization in the first direction is possible between the motor 21 and the drive circuit 32. Therefore, it is possible to easily determine whether the energization in the first direction is possible.

Note that the embodiment may be changed as explained below.

In the embodiment, when the phase induced voltage value ex is equal to or smaller than the energization determination threshold e_pd, it is determined that the energization in the first direction is possible. However, the determination is not limited to this. An energization failure may be determined prior to the detection of the open malfunction and it may be determined that the energization in the first direction is possible on condition that an energization failure has not occurred. In this configuration, when a determination result of the energization failure is used, it is unnecessary to separately perform determination as to whether the energization in the first direction is possible.

In the embodiment, other conditions such as whether a power supply voltage of the vehicle-mounted power supply 36 is equal to or larger than a value for enabling application of a sufficient voltage to the motor 21 may be added to the determination of the energization failure.

In the embodiment, the phase induced voltage values eu, ev, and ew are used as the voltage parameters equivalent to the voltage applied to the motor 21. However, the phase voltage command values Vu*, Vv*, and Vw*, the DUTY command values αu, αv, and αw, the phase voltage values Vu, Vv, and Vw detected by the voltage sensors 38 u, 38 v, and 38 w, or the like may be used.

In the embodiment, during the high-speed rotation determination, the abnormality detecting unit 71 determines whether the phase induced voltage values ey and ez of the other phases are equal to or smaller than the high-speed determination threshold e_him while the sign of the phase induced voltage value ex is plus in the one cycle of electrical angle before the change of the sign of the phase induced voltage value ex of the specific phase to minus. However, in addition to the determination performed while the sign of the phase induced voltage value ex is plus, the abnormality detecting unit 71 may determine whether the phase induced voltage values ey and ez of the other phases are equal to or larger than the high-speed determination threshold e_hip while the sign of the phase induced voltage value ex is minus.

In the embodiment, the abnormality detecting unit 71 determines on the basis of the phase induced voltage value eu, ev, and ew whether the motor 21 is rotating at high speed. However, the abnormality detecting unit 71 may estimate motor rotation angular velocity on the basis of the motor rotation angle θm detected by the rotation angle sensor 40 and determine on the basis of the motor rotation angular velocity whether the motor 21 is rotating at high speed.

In the embodiment, the high-speed determination thresholds e_hip and e_him are set to the values smaller than the energization determination threshold e_pd and the abnormality determination threshold e_er. However, the high-speed determination thresholds e_hip and e_him may be set to values equal to or larger than the energization determination threshold e_pd and the abnormality determination threshold e_er.

In the embodiment, the MOSFETs are used as the relay FETs 39 u, 39 v, and 39 w functioning as the phase open switches. However, the relay FETs 39 u, 39 v, and 39 w only have to be phase open switches including parasitic diodes. For example, junction FETs or the like may be used.

In the embodiment, the relay FETs 39 u, 39 v, and 39 w are provided such that the parasitic diodes D allow the energization in the first direction. However, the relay FETs 39 u, 39 v, and 39 w may be provided such that the parasitic diodes D allow the energization in the second direction.

In the embodiment, the abnormality detecting unit 71 simultaneously executes the abnormality detection for the three phases in parallel. However, the abnormality detecting unit 71 may sequentially execute the abnormality detection for each of the phases.

The present invention may be embodied as a motor control device that controls other motors such as a motor of a transmission ratio variable device that transmits rotation based on motor driving to an output shaft in addition to rotation of an input shaft based on steering operation using a differential mechanism. 

The invention claimed is:
 1. A motor control device comprising: motor control signal output means for outputting a motor control signal; a drive circuit configured to supply drive power of three phases to a motor on the basis of the motor control signal; phase open switches provided in power lines of respective phases that connect the motor and the drive circuit; and abnormality detecting means for detecting an open malfunction of the phase open switches on the basis of a voltage parameter equivalent to a voltage applied to the motor, the motor control signal output means outputting the motor control signal by executing current feedback control in order to cause an actual current value to follow a current command value, which is a target value of an electric current supplied to the motor, wherein: the phase open switches include parasitic diodes that allow energization in a first direction in an OFF state for cutting off energization to phases corresponding to the phase open switches, the abnormality detecting means uses, as the voltage parameter, phase induced voltage value of the respective phase of motor calculated on the basis of phase current value and phase voltage value of the respective phase of motor and in a state in which the energization in the first direction is possible between the motor and the drive circuit and the motor is not rotating at high speed, when the phase induced voltage values of a specific phase set as a determination target increases to a side for feeding an electric current in a second direction in which energization is not allowed by the parasitic diodes and exceeds an abnormality determination threshold, the abnormality detecting means determines that an open malfunction has occurred in the phase open switch of the specific phase, wherein in a state in which the motor is rotating at high speed, even if an open malfunction has not occurred, an electric current cannot be fed to the motor because of the influence of an induced voltage.
 2. The motor control device according to claim 1, wherein the abnormality detecting means determines whether the motor is rotating at high speed when a sign of the phase induced voltage value of the specific phase changes from a sign indicating feeding of an electric current in the first direction to a sign indicating feeding of an electric current in the second direction, and when the phase induced voltage value of at least one phase among the phases other than the specific phase exceeds a high-speed determination threshold based on an induced voltage, which occurs during high-speed rotation, in one cycle of electrical angle before the change of the phase induced voltage value of the specific phase to the sign indicating feeding of an electric current in the second direction, the abnormality detecting means determines that the motor is rotating at high speed.
 3. The motor control device according to claim 2, wherein, when the phase induced voltage value of at least one phase of the other phases exceeds the high-speed determination threshold while the sign of the phase induced voltage value of the specific phase in the one cycle of electrical angle is the sign indicating feeding of an electric current in the first direction, the abnormality detecting means determines that the motor is rotating at high speed.
 4. The motor control device according to claim 1, wherein, when the phase induced voltage value is equal to or smaller than an energization determination threshold set to a side for feeding an electric current in the first direction, the abnormality detecting means determines that the energization in the first direction is possible between the motor and the drive circuit.
 5. The motor control device according to claim 1, wherein, when an energization failure does not occur in a power supply route between the motor and the drive circuit, the abnormality detecting means determines that the energization in the first direction is possible between the motor and the drive circuit.
 6. A steering device for a vehicle comprising the motor control device according to claim
 1. 7. A motor control device comprising: motor control signal output unit that outputs a motor control signal; a drive circuit configured to supply drive power of three phases to a motor on the basis of the motor control signal; phase open switches provided in power lines of respective phases that connect the motor and the drive circuit; and abnormality detecting unit that detects an open malfunction of the phase open switches on the basis of a voltage parameter equivalent to a voltage applied to the motor, the motor control signal output unit outputting the motor control signal by executing current feedback control in order to cause an actual current value to follow a current command value, which is a target value of an electric current supplied to the motor, wherein: the phase open switches include parasitic diodes that allow energization in a first direction in an OFF state for cutting off energization to phases corresponding to the phase open switches, the abnormality detecting means uses, as the voltage parameter, phase induced voltage value of the respective phase of motor calculated on the basis of phase current value and phase voltage value of the respective phase of motor and in a state in which the energization in the first direction is possible between the motor and the drive circuit and the motor is not rotating at high speed, when the phase induced voltage values of a specific phase set as a determination target increases to a side for feeding an electric current in a second direction in which energization is not allowed by the parasitic diodes and exceeds an abnormality determination threshold, the abnormality detecting unit determines that an open malfunction has occurred in the phase open switch of the specific phase, wherein in a state in which the motor is rotating at high speed, even if an open malfunction has not occurred, an electric current cannot be fed to the motor because of the influence of an induced voltage.
 8. The motor control device according to claim 7, wherein the abnormality detecting unit determines whether the motor is rotating at high speed when a sign of the phase induced voltage value of the specific phase changes from a sign indicating feeding of an electric current in the first direction to a sign indicating feeding of an electric current in the second direction, and when the phase induced voltage value of at least one phase among the phases other than the specific phase exceeds a high-speed determination threshold based on an induced voltage, which occurs during high-speed rotation, in one cycle of electrical angle before the change of the phase induced voltage value of the specific phase to the sign indicating feeding of an electric current in the second direction, the abnormality detecting unit determines that the motor is rotating at high speed.
 9. The motor control device according to claim 8, wherein, when the phase induced voltage value of at least one phase of the other phases exceeds the high-speed determination threshold while the sign of the phase induced voltage value of the specific phase in the one cycle of electrical angle is the sign indicating feeding of an electric current in the first direction, the abnormality detecting unit determines that the motor is rotating at high speed.
 10. The motor control device according to claim 7, wherein, when the phase induced voltage value is equal to or smaller than an energization determination threshold set to a side for feeding an electric current in the first direction, the abnormality detecting unit determines that the energization in the first direction is possible between the motor and the drive circuit.
 11. The motor control device according to claim 7, wherein, when an energization failure does not occur in a power supply route between the motor and the drive circuit, the abnormality detecting unit determines that the energization in the first direction is possible between the motor and the drive circuit.
 12. A steering device for a vehicle comprising the motor control device according to claim
 7. 